The invention relates to a bone cement based on physiologically tolerated polymers, in particular on polyacrylates and/or polymethacrylates prepared from prepolymers and monomers, and to a process for mechanically disrupting fully polymerized plastics, in particular these bone cements.
A central problem in the implantation of joint endoprostheses is the anchorage of the prosthesis in the bone substrate. For this purpose, it is known to use bone cements which are based on acrylate and which are prepared by mixing and fully polymerizing pulverulent prepolymers with liquid monomers containing initiators and accelerators for the polymerization. These are used in orthopaedic surgery for the reliable and rapid primary fixing of the joint implant to the bone, thus enabling the patient to put a load on the joint at an early stage. The bone cement, which initially is still pasty in the mixing phase and cures slowly, fills the space between the bone and the joint implant almost without any gaps, but very rapidly gains its full strength as a result of the continuing polymerization process.
This type of fixing joint endoprostheses to the bone by means of fully polymerized bone cement is nowadays a surgical technique which is used and recognized throughout the world in orthopaedic surgery. Problems such as excessive liberation of energy and hence an unduly high temperature during the polymerization, whch leads to necrotization of the tissue, have been solved in principle, as have the questions of adequate biocampatibility of the bone cement.
In the long term, however, loosening of the metal implant or of the plastic implant in the bone cement substrate can occur, so that prosthesis replacements with removal of the bone cement become necessary. The removal of the bone cement from tubular bones is technically very difficult and involves a long operating time in the case of re-operations of joint endoprostheses, so that the predominantly old patients are put at considerable risk by long operating times, long bleeding times of the exposed soft tissues and an increased danger of infection due to long times with an open wound. The importance of this problem can be gauged by the fact that up to 20% of all joint prosthesis operations carried out nowadays are re-operations.